It seems crazy OP, even for a legendary. The anti-resurrection magic is a sideshow; the real story is the insane damage it does: 1d4 (piercing)+3d12(necrotic) per hit, (23 average damage, before any other bonuses)! I don't care if you're the beefiest barbarian that ever lived, this dagger is your best in slot weapon!

A level 20 fighter with this blade, assuming duelist and 20 strength, is going to have an opening round, with action surge, of 8 attacks averaging 30 damage each. Without critical hits, which could be huge on this weapon. And is still using a shield.

That's dumb.